JPH0739932B2 - Grating interference displacement detector - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grating interference type displacement detecting device. More specifically, a grating interference type displacement detection in which a light flux from a light source is split into two waves and is made incident on different diffraction points on a diffraction grating of a scale, and a mixed wave of the light fluxes generated at each diffraction point is detected as an electric signal. The present invention relates to a device, and more particularly, to a device that prevents return light to a light source.

[0002]

BACKGROUND ART As one of the ones aiming at higher resolution of a conventional photoelectric encoder, a scale having a fine pitch (usually about 1 μm) is formed on a scale by using a holographic technique, and the scale is used as a diffraction grating. There is known a grating interference type displacement detection device which utilizes the above to detect relative displacement with high accuracy. This is a method in which a light beam from a light source is split into two waves, made incident on one or two diffraction points on the diffraction grating of the scale, and a mixed wave of a plurality of light beams generated at the diffraction points is detected as an electric signal. Then, with the one using a reflection type diffraction grating,
It can be classified into one using a transmission type diffraction grating.

As the former, a grating interference type displacement detecting device using a reflection type diffraction grating, as shown in FIG. 2, a reflection type diffraction grating 2A is provided so as to be displaceable in the left and right direction in the figure and along the displacement direction. The reflective scale 1A, the laser light source 11, the half mirror 24 that splits the laser beam emitted from the laser light source 11 into two waves A and B, and the branched light fluxes A and B are reflected to diffract the scale 1A. A pair of mirrors 23A and 23B which are incident on the same diffraction point P on the grating 2A from symmetrical directions respectively, and a mirror 32 which reflects the first-order diffracted lights A1 and B1 emitted right above at the diffraction point P right below.
And the reflected light from the scale 1A and the mirrors 23A and 23B.
And a detector 41 for converting the mixed wave mixed through the half mirror 24 into an electric signal. Here, the half mirror 24 and the pair of mirrors 23
A luminous flux splitting means 21 is constituted by A and 23B, and a luminous flux mixing means 31 is constituted by the half mirror 24, a pair of mirrors 23A and 23B, and a mirror 32.

Therefore, the laser beam from the laser light source 11 is divided into two by the half mirror 24. After each of the branched light fluxes A and B is reflected by each of the mirrors 23A and 23B,
The light is incident on the same diffraction point P on the diffraction grating 2A of the scale 1A from symmetrical directions. Then, the first-order diffracted lights A1 and B1 of the respective branched light beams A and B are generated at the diffraction point P. The first-order diffracted lights A1 and B1 are sequentially reflected by the mirror 32, the scale 1A, and the pair of mirrors 23A and 23B, then mixed by the half mirror 24, and guided to the detector 41. In the detector 41, the polarization directions of the mixed waves mixed by the half mirror 24 are matched by the polarizing plates to cause interference, and then converted into electric signals by the light receiving element. As a result, the detector 4
From 1, when the scale 1A is displaced by one pitch of the diffraction grating 2A, a complete sine wave signal φA for two cycles is obtained.

As the latter grating interference type displacement detecting device using the transmission type diffraction grating, as shown in FIG. 3, a transmission type diffraction grating 2B is provided so as to be displaceable in the left and right directions in the figure and along the displacement direction. The transmission type scale 1B has, a laser light source 11, a polarization beam splitter 22 that splits a laser beam emitted from the laser light source 11 into two waves A and B according to the deflection direction thereof, and reflects each branched light flux A and B. And a pair of mirrors 23A and 23B which are incident on the same diffraction point P on the diffraction grating 2B of the scale 1B from symmetrical directions respectively.
, A mirror 32 for directly reflecting the first-order diffracted light A1, B1 generated at the diffraction point P, a beam splitter 34 for mixing the reflected light, and detectors 41A, 41B for converting the mixed wave into an electric signal. It consists of and. here,
The polarization beam splitter 22 and the pair of mirrors 23
A and 23B constitute a light beam splitting means 21, and the mirror 32 and the beam splitter 34 constitute a light beam mixing means 31, respectively.

Therefore, the laser beam from the laser light source 11 is divided into two beams according to the polarization direction of the polarization beam splitter 22.
Be divided. The respective branched light fluxes A and B are transmitted to the respective mirrors 23A and 23
After being reflected by B, they are respectively incident on the same diffraction point P on the diffraction grating 2B of the scale 1B from symmetrical directions. Then, at the diffraction point P, the first-order diffracted light A1, of each branched light flux A, B
B1 is generated. The first-order diffracted lights A1 and B1 are reflected by the mirror 3
It is reflected right above by 2 and then mixed by the beam splitter 34 and then guided to the detectors 41A and 41B. In the one detector 41A, the polarization directions of one of the mixed waves mixed in the beam splitter 34 are matched by the polarizing plates to cause interference, and then converted into an electric signal by the light receiving element. In the other detector 41B, the beam splitter 3
The other mixed wave mixed in 4 is delayed in phase by 90 degrees with respect to the mixed wave incident on the one detector 41A by the quarter wavelength plate, and then the polarization direction of the mixed wave is matched by the polarizing plate. After making them interfere with each other, they are converted into electric signals by the light receiving element. Thereby, each detector 41A, 41B
From the above, when the scale 1B is displaced by one pitch of the diffraction grating 2B, complete sine wave signals φA and φB for two periods having different 90 ° phase differences are obtained.

[0007]

However, in any of the above-mentioned grating interference type displacement detecting devices, the branched light beams A and B are obliquely incident on the scales 1A and 1B and are perpendicular to the scales 1A and 1B. Since it is an optical system that reflects and diffracts light in the direction, there is return light to the laser light source 11. In order to remove this, a polarizing element, a wave plate, etc. are required, and even if these are provided, it is difficult to completely remove the return light, so the output from the laser light source becomes unstable. There is a drawback that.

Further, all of the above-mentioned devices have a large number of parts and are required to be assembled, because they require a plurality of types of optical elements.
There is a problem that the adjustment takes time and the device becomes large. Particularly, in the case of the latter transmission type diffraction grating 2B, the laser light source 11, the light beam splitting means 21, and the scale 1B are sandwiched therebetween.
Since the mirror 32 must be arranged on the side opposite to the optical system such as the light flux mixing means 31 and the detectors 41A and 41B, there is a problem that it is difficult to incorporate the mirror 32 into the apparatus.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art, to completely eliminate the return light to the light source, and to assemble and adjust the grating interference type displacement detecting device easily. To provide.

[0010]

Therefore, the grating interference type displacement detecting apparatus of the present invention includes a scale having a reflection type diffraction grating, a light source, and a spectroscopic element for splitting a light beam from the light source into two waves. A light beam splitting unit that makes the split light beams incident on different diffraction points on the diffraction grating of the scale, a light mixing element that mixes the light beams generated at each diffraction point, and a mixed wave that is mixed by the light mixing element is electrically generated. In a grating interference type displacement detection device including a detector for converting into a signal, the spectroscopic element and the light mixing element are constituted by a prism, and each branched light flux branched into two waves by the spectroscopic element is formed on a side surface of the prism. Forming a reflective / transmissive surface that reflects at different diffraction points on the diffraction grating of the scale and transmits the mixed wave mixed by the light mixing element. And was different from the transmission point of the mixed wave and the reflection point of each branched light beam in the reflection and transmission plane, characterized in that.

[0011]

The light flux from the light source is first reflected by the spectroscopic element.
After being split into waves, they are reflected by the reflection / transmission surface of the integral prism and are incident on different diffraction points on the diffraction grating of the scale. Then, at each diffraction point, first-order diffracted light whose phases are shifted in opposite directions is generated. The respective first-order diffracted lights are mixed by the light mixing element and then transmitted through the reflection / transmission surface of the prism to be incident on the detector. At this time,
Since the reflection point of each branched light beam and the transmission point of the mixed wave are different, the return light to the light source can be removed. Moreover, since the spectroscopic element and the light mixing element are constituted by the prism, the number of parts can be reduced and the assembly and adjustment can be easily performed.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the grating interference type displacement detector according to the present invention will be described below in detail with reference to the accompanying drawings. In the following description, the same components as those in FIGS. 2 and 3 described above will be designated by the same reference numerals, and the description thereof will be omitted or simplified.

FIG. 1 shows a grating interference type displacement detector of this embodiment. In the same grating interference type displacement detection device, the light beam splitting means 21 and the light beam mixing means 31 are constituted by an integral prism 51. A polarizing beam splitter 22 as a spectroscopic element for splitting the laser beam from the laser light source 11 into two waves A and B according to the deflection direction of the laser beam and a beam splitter 34 as a light mixing element are provided at a central position inside the prism 51. Each is provided. Further, on both side surfaces, the branched light beams A and B branched by the polarization beam splitter 22 are reflected in the direction perpendicular to the scale 1A and are made incident on different diffraction points Pa and Pb on the diffraction grating 2A, respectively. The beam splitter 34
Reflective / transmissive surfaces 51A and 51B for transmitting the mixed wave of the first-order diffracted lights A1 and B1 mixed by are formed.

Here, on the reflection / transmission surfaces 51A and 51B, the reflection points Qa and Qb of the branched light fluxes A and B and the transmission points Ra and Rb of the mixed wave of the first-order diffracted lights A1 and B1 are different from each other. Reflective / transmissive surfaces 51A and 51B are formed. The polarization beam splitter 22 and the reflective / transmissive surfaces 51A and 51B constitute the light beam splitting means 21 of this embodiment. Also, the beam splitter 3
4 constitutes the light flux mixing means 31 of the present embodiment.

Due to such a constitution, the laser light source 1
The laser beam emitted from No. 1 is split into two waves A and B by the polarization beam splitter 22. The branched luminous fluxes A and B are respectively reflected and transmitted surfaces 51A and 51A of the prism 51.
After being reflected by 51B, it is incident on different diffraction points Pa and Pb on the diffraction grating 2A of the scale 1A. Then, the first-order diffracted lights A1 and B1 of the branched luminous fluxes A and B are generated at the diffraction points Pa and Pb, respectively. First-order diffracted light A1, B1
Are mixed in the beam splitter 34.

That is, the reflected light of one first-order diffracted light A1 and the transmitted light of the other first-order diffracted light B1 are mixed, and the transmitted light of one first-order diffracted light A1 and the reflected light of the other first-order diffracted light B1 are mixed. And are mixed. After that, one of the mixed waves passes through the reflection / transmission surface 51A and is guided to the one detector 41A, where it is converted into an electric signal and taken out as a sine wave signal φA. The other mixed wave is transmitted through the reflection / transmission surface 51B and guided to the other detector 41B, where the phase is delayed by 90 degrees with respect to the one mixed wave.
It is converted into an electric signal and taken out as a sine wave signal φB.

Therefore, according to this embodiment, after the laser beam is split into two waves A and B by the polarization beam splitter 22, the laser beam is reflected by the reflection / transmission surfaces 51A and 51B, and the two different wavelengths on the diffraction grating 2A of the scale 1A. Two diffraction points P
It is made incident on a and Pb. First-order diffracted lights A1 and B generated at the diffraction points Pa and Pb and phase-shifted in mutually opposite directions.
After 1 is mixed by the beam splitter 34, it is transmitted through the reflection / transmission surfaces 51A and 51B and is incident on the detectors 41A and 41B, and the reflection points Qa and Qb of the respective branched light fluxes A and B on the reflection / transmission surfaces 51A and 51B. And the first-order diffracted light A1,
Since the transmission points Ra and Rb through which the mixed wave of B1 is transmitted are made different, the return light to the light source 11 can be removed.

The beam splitting means 21 and the beam mixing means 3 are also provided.
1, that is, the polarization beam splitter 22, the beam splitter 34, and the reflection / transmission surface 51A,
Since 51B and the like are configured by the integral prism 51,
The main detection system can be configured by one prism. This leads to a reduction in the number of parts, so that the assembly and adjustment can be easily performed, and the cost can be reduced.

Moreover, the light source 1 is provided on one side of the scale 1B.
1. Since all the optical systems such as 1, the light beam splitting unit 21, the light beam mixing unit 31, and the detectors 41A and 41B are arranged, they can be easily incorporated into the apparatus.

Although the present invention has been described with reference to the preferred embodiment, the present invention is not limited to this embodiment, and various improvements and design changes can be made without departing from the gist of the present invention. Of course it is possible.

For example, in the above embodiment, the polarization beam splitter 22, the beam splitter 34 and the reflection / transmission surface 5 are used.
1A, 51B and the like are configured by the integral prism 51, but may be configured by combining a plurality of prism elements.

In the above embodiment, the laser light source 11,
Light flux splitting means 21, light flux mixing means 31, and detector 41
Although the scale 1A is provided so as to be displaceable with respect to the optical systems such as A and 41B, the optical system may be displaced with respect to the scale 1A, or both may be displaced. In short, the present invention can be applied to all scales in which the scale 1A and the optical system are displaced relative to each other.

[0023]

As described above, according to the displacement detecting apparatus of the grating interference type of the present invention, the return light to the light source can be removed, and the assembly and the adjustment can be easily performed.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a grating interference type displacement detection device of the present invention.

FIG. 2 is a diagram showing a conventional grating interference type displacement detection device (using a reflection type diffraction grating).

FIG. 3 is a diagram showing a conventional grating interference type displacement detection device (using a transmission type diffraction grating).

[Explanation of symbols]

 1A Reflective Scale 2A Reflective Diffraction Grating 11 Laser Light Source (Light Source) 21 Luminous Flux Splitting Unit 22 Polarizing Beam Splitter (Spectroscopic Element) 34 Beam Splitter (Light Mixing Element) 41A, 41B Detector 51 Prism 51A, 51B Reflective Transmission Surface Pa, Pb Diffraction point Qa, Qb Reflection point Ra, Rb Transmission point

Claims (1)

[Claims] 1. A scale having a reflection type diffraction grating, a light source, and a spectroscopic element that splits a light beam from the light source into two waves, and each branched light beam is made incident on different diffraction points on the diffraction grating of the scale. In a grating interference type displacement detection device provided with a light beam splitting means, a light mixing element for mixing light beams generated at respective diffraction points, and a detector for converting a mixed wave mixed by the light mixing element into an electric signal The light-splitting element and the light mixing element are configured by a prism, and the branched light beams split into two waves by the light-splitting element on the prism side surface are respectively reflected at different diffraction points on the diffraction grating of the scale and A reflective / transmissive surface that transmits the mixed wave mixed by the mixing element is formed, and the reflection point of each branched light flux on the reflective / transmissive surface and the mixed wave A grating interference type displacement detection device characterized in that the transmission point is different.